Digital multichannel multipoint distribution system (MMDS) network that supports broadcast video and two-way data transmissions

ABSTRACT

The present invention comprises a MMDS broadcast digital video cell system on one polarization and a smaller array of cells, designed for two way services that use the orthogonal polarization in the same area. The present invention includes a method for distributing information in a MMDS network comprising the steps of providing a video signal in a first polarization to a first area, the video signal having a frequency within a predetermined set of frequencies, the method further includes providing a two-way digital signal in a second polarization to the first area, the two-way digital signal having a frequency within the predetermined set of frequencies, wherein the second polarization is orthogonal to the first polarization. The present invention also includes a system for distributing information in a MMDS network comprising a digital video signal transmitter, wherein the video signal has a first polarization. In addition, the video signal has a first frequency within a predetermined set of frequencies. The system also includes a digital video signal receiver at a receiver site and a digital communication signal transmitter for transmitting communication signals wherein the communication signal has a second polarization. The communication signal has a frequency within the same predetermined set of frequencies. Finally, a digital communication signal receiver is located at the receiver site.

FIELD OF THE INVENTION

The present invention relates generally to the distribution ofinformation on a wireless communications network and more particularlyto the distribution of communication information on a MMDS network.

BACKGROUND OF THE INVENTION

Video information is distributed over a communications network generallyin two conventional ways (wireless (i.e., MMDS) and wireline (CATV)).Either of these services can be analog or digital.

A conventional wireless video signal is transmitted in a predeterminedfrequency range from a one-way broadcast video transmission site in afirst polarization (i.e., either horizontal or vertical). The wirelessvideo signal is then received at a customer site in the samepolarization, via a video antenna.

To more particularly describe a conventional MMDS video distributionsystem, refer now to FIG. 1.

FIG. 1 is a block diagram of a conventional video distribution system100 which, for example, operates over a range of up to 35 miles. A videosignal is transmitted from a broadcast video transmission site 106 by anantenna 102 in a given polarization such as horizontal polarization. Inthis system, the antenna 102 is designed such that cross-polarizationpolarization rejection is typically at some minimum value such as 20dB.Accordingly, the effective radiated power of this transmitter may be upto hundreds of Watts. The video signal is then received in the same(horizontal) polarization by a video antenna 108 at a customer site 104.

One conventional frequency range that video signals are transmitted insuch a system is between 2150-2162 Mhz and 2500-2686 MHz (i.e., 33 6 MHzchannels). This frequency spectrum is referred to as a multichannelmultipoint distribution system (MMDS).

Background information regarding local multipoint distribution systems(LMDS) (28 GHz) with details of cellular techniques, polarizationdiversity, spatial diversity, and frequency reuse can be found in U.S.Pat. No. 4,747,160, issued May 24, 1988 to Bossard. Backgroundinformation regarding point-to-multipoint radio communication systemincluding a master station and a plurality of remote stations whichcommunicate with the master station using frequency divisionmultiplexing can be found in U.S. Pat. No. 4,528,656, issued Jul. 9,1985 to Morais. Other patents that discuss polarized modulation or theuse of horizontal and vertical polarization in the context of radiotransmissions include U.S. Pat. No. 2,992,427, issued Jul. 11, 1961 toFranco; U.S. Pat. No. 3,882,393, issued May 6, 1975 to Epstein; U.S.Pat. No. 4,220,923, issued Sep. 2, 1980 to Pelchat et al.; U.S. Pat. No.4,321,705, issued Mar. 23, 1982 to Namiki; and U.S. Pat. No. 4,521,878,issued Jun. 4, 1985 to Toyonaga. Finally, U.S. Pat. Nos. 3,864,633,issued Feb. 4, 1975 to Stenglein, and 4,525,861, issued Jun. 25, 1985 toFreeburg may be of general relevance.

In analog MMDS systems, as before mentioned, the response channels fromthe customer site have been limited (typically by FCC regulation) to asmall bandwidth (125 kHz wide) for voice or data transmission. Thebandwidth of these response channels severely limits their use totransmit information from the customer site to the transmission site.The use of the frequencies are restricted typically by the communicationauthorities.

Accordingly, what is needed is a system and method for allowing moreinformation to be distributed over a digital MMDS network. The systemand method should be easily implemented, cost effective and easilyadaptable to existing communication networks. The present inventionaddresses such a need.

SUMMARY OF THE INVENTION

The present invention comprises a MMDS broadcast digital video cellsystem on one polarization and a smaller array of cells, designed fortwo way services that use the orthogonal polarization in the same area.

The present invention includes a method for distributing information ina MMDS network comprising the steps of providing a video signal in afirst polarization to a first area, the video signal having a frequencywithin a predetermined set of frequencies, the method further includesproviding a two-way digital signal in a second polarization to the firstarea, the two-way digital signal having a frequency within thepredetermined set of frequencies, wherein the second polarization isorthogonal to the first polarization.

The present invention also includes a system for distributinginformation in a MMDS network comprising a digital video signaltransmitter, wherein the video signal has a first polarization. Inaddition, the video signal has a first frequency within a predeterminedset of frequencies. The system also includes a digital video signalreceiver at a receiver site and a digital communication signaltransmitter for transmitting communication signals wherein thecommunication signal has a second polarization. The communication signalhas a frequency within the same predetermined set of frequencies.Finally, a digital communication signal receiver is located at thereceiver site.

The present invention allows the network operators to provide greaterthan 295 channels (3Mb/s each) of digital broadcast video simultaneouslywith a complete two-way service using the same spectrum in the sameprotected service area as those used for the digital broadcast video.The two-way service can include telephony, video conferencing, andinternet access.

The cross-polarization technique and the overlay network design will bemore fully understood by reference to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a standard one-way multichannel analog ordigital video distribution system typically operating over a range of upto thirty-five miles.

FIG. 2 is a conceptual diagram of a top plane view of an overlay networkusing the cross polarization technique according to the presentinvention.

FIG. 3A is a top plane view illustrating one of the possible frequencyreuse plans for the two-way digital service network according to thepresent invention.

FIG. 3B is a top plane view illustrating an alternative frequency reuseplan for the two-way digital service network according to the presentinvention.

FIG. 4 illustrates the frequency band of a typical MMDS network. It alsoprovides an example of a possible frequency allocation for a four-foldfrequency reuse data system.

FIG. 5 depicts the overlay of the two-way service network with thedigital video service, thus allowing both services to be simultaneouslyreceived by the customer.

FIG. 6 is a schematic diagram of the network cell site location and itsfunctionality.

FIG. 7A shows a system and method of reception of digital video at thecustomer site.

FIG. 7B shows a system and method of reception at the customer siteafter data is received on the vertically polarized two-way antenna.

FIG. 7C shows a system and method of the uplink path from the customerdata device (e.g., computer) to the vertically polarized two-wayantenna.

FIG. 8 is a table of an example of link budgets for both the digitalvideo service and the two-way data/telephony.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a distribution of information in acommunications system. The following description is presented to enableone of ordinary skill in the art to make and use the invention and isprovided in the context of a patent application and its requirements.Various modifications to the preferred embodiment will be readilyapparent to those skilled in the art and the generic principles hereinmay be applied to other embodiments. Thus, the present invention is notintended to be limited to the embodiment shown but is to be accorded thewidest scope consistent with the principles and features describedherein.

A system and method according to the present invention is a two-waydigital network using a polarization orthogonal to the polarization of alarger digital broadcast video cell system

The present invention can be thought of as a digital cellular networkthat is overlaid onto a digital broadcast video network. The digitaloverlay network is preferably completely autonomous from the broadcastvideo network, and in this way, leverages the entire spectrum for bothservice offerings. The interference between the broadcast video and theservices network can be minimized through the use of polarizationdiversity techniques.

The method and system according to the present invention allows both thetwo-way digital "cellular" network and the digital broadcast videonetwork to use the entire available spectrum simultaneously. An exampleof a spectrum which can be utilized with the present invention is theMMDS spectrum. Assuming the MMDS operator has access to all 33 licenses(i.e., 33 6 MHz channels), the present invention would allow the MMDSoperators to provide greater than 295 channels (3 Mb/s each) of digitalbroadcast video along with a complete two-way service offering,including telephone, video conferencing, internet access, etc. in thesame protected service area, which is typically thirty-five miles.

FIG. 2 is a conceptual diagram of a top plane view of an overlay networkusing the cross polarization technique according to the presentinvention. It includes a broadcast digital video cell system 200 whichuses one polarization, such as horizontal. In the case of a video cellsystem 200 utilizing the MMDS spectrum, the cell 200 would typicallyencompass an area with five to thirty-five mile radii.

The digital video cell system 200 is overlaid with an array of two-waycells 202 within the same licensed area. The array of two-way cells 202is designed for two-way services that uses a different polarization fromthe one used for the digital video cell system 200. Assuming the digitalvideo cell system 200 uses a horizontal polarization, the two-way cells202 would use vertical polarization. This allows the entire spectrum inthe typical thirty-five mile protected service area to be used for boththe two-way service network as well as the digital broadcast network,while allowing for significant simplicity and flexibility in bothnetwork designs.

Transmit and receive antennas in both networks are preferably selectedwith high cross polarization specifications. In this way the operatorhas the ability to design two different networks, that through suitablemodulation and link margins, should substantially decrease anyinterference between the two systems.

The two-way network system and method according to the present inventionis based on a cellular array approach which could use a variety oftwo-way cell 202 designs. Two embodiments of two-way cell 202 designsare shown in FIGS. 3A and 3B. Both designs use a four-fold frequencyreuse pattern.

FIG. 3A is a top plane view illustrating one of the possible frequencyreuse plans for the two-way digital service network according to thepresent invention. A video cell system 200' is overlaid with an array oftwo-way cells 202'. The array of two-way cells 202' include a pluralityof two-way cells 202'a-202'd that use varying frequency bands. Thisapproach uses the same frequency band throughout the entire cell 202'afor the downstream data. It is surrounded by only those cells202'b-202'd with the other three frequency bands in order to minimizeinterference.

FIG. 4 illustrates the frequency channels of a typical MMDS network. Asshown in FIG. 4, each frequency band can be as much as 48 MHz, with theexception of the fourth, which can be 42 MHz.

FIG. 3B is a top plane view illustrating an alternative four-foldfrequency reuse plan for the two-way digital service network accordingto the present invention. The video cell system 200" is overlaid withtwo-way cells 202", where each two-way cell 202" is divided into foursectors or quadrants 202"a-202"d, where each quadrant 202"a-202"d hasits own frequency band. Of course, increasing the number of sectors andfrequency reuse is also possible depending on desired capacities andlink margins (i.e., 12-fold and 30 degree sectors).

The selection of one method over the other would depend on variousfactors such as demographics, licenses, the topography, the selected RFhardware, and the link budgets. The response path (upstream) for thetwo-way service can use MDS 1 and MDS 2 in each cell (two channels2150-2162 MHz). But again, any portion of the MMDS spectrum could beused for upstream service.

FIG. 5 depicts the addition (or overlay) of the two-way service networkwith the digital video service, thus allowing both services to besimultaneously received by the customer. FIG. 5 shows a system andmethod of a two-way network 300 according to the present invention. Thevideo signal is sent from the one-way broadcast digital videotransmission site 312 via the digital video antenna 314. The videotransmission site 312 is typically up to 35 miles from the customer site306. The two-way network 300 includes a two-way service network cellsite 302, a cell site antenna 304 which transmits to a customer site306. The customer site 306 includes a two-way antenna 310 for receiptand transmission of two-way signals, and a video antenna 308 for receiptof video signals. The network cell site and subscriber site can belocated in one of the two-way cells 202 of FIG. 2.

The network cell site 302 transmits data on a polarization orthogonal tothe video signal via the cell site antenna 304. In this example, thevideo signal has a horizontal polarization while the network cell site302 transmits on a vertical polarization. The two-way antenna 304located on the network cell site 302 is preferably a verticallypolarized receiving antenna with similar specification of gain andcross-polarization as the customer receive antennas 310.

At the customer site 306, the video antenna 308 is used simultaneouslywith the two-way antenna 310. The horizontally polarized video antenna308 receives the digital video signals while the vertically polarizedtwo-way antenna 310 transmits and receives the two-way services such asdata/telephonic services.

Each video antenna 308 of FIG. 5 used for receiving the digitalbroadcast video (video cells system 200 of FIGS. 2 and 3 with 5-35 mileradii) would preferably have antenna gains higher than 15 dBi, a crosspolarization specification approaching 30 dB at the boresight, andsidelobes that are at least 18 dB down from the main lobe.

All the receive antennas 304, 310, 308 of FIG. 5 and matchingdownconverters 500, 520 would also preferably be designed to receive theentire 33 channels, two between 2150-2162 MHz and thirty-one between2500-2686 MHz. The modulation of the digital video can be any higherorder modulation, N-QAM (Quadrature Amplitude Modulation) or N-VSB(Vestigial Side Band) (i.e., 64 QAM). Sixty-four level QAM chips withReed Solomon Forward Error correction can provide approximately 27 Mb/sof information payload per 6 MHz channels with a signal to noisethreshold of 24.5 dB (correct BER 10⁻⁹).

Each receive two-way antenna 310, 304 used for the two-way digitalservices should preferably have specifications for gain, crosspolarization and side lobes comparable to the digital video receiveantennas 308. This will allow flexibility in designing the two-waydigital network (typical cell 202 radii of one to seven milesnominally).

The transmit antennas 314 for the digital video broadcast and thetwo-way network can be omnidirectional or directional, but wouldpreferably also meet a cross polarization specification of 30 dB.

A schematic diagram of an example of the data network cell (head end)site location 302 and its functionality is shown in FIG. 6. It includesa gateway and router 402, a switch 406, application servers 404, networkcontrol computer 408, an administration computer 410, a network elementmanager 412, encryption/encoding 414, decoding decryption 416,modulators 418a-418d, and a combiner 420.

The cell site input for the data service arrives from a content providersuch as the Internet. After passing through the gateway and router 402,it passes to a switch 406, such as an asynchronous transfer mode (ATM)switch. There can be numerous control mechanisms that provide functionssuch as fault detection, error reporting, billing, and authorizations.The application servers 404 may hold navigation programs, bankingprograms, or other applications. The output data from the switch 406 foreach particular user is then encrypted for security and encoded forforward-error-correction via encryption/encoding 414. This is followedby the N-QAM modulator 418. After the signals for all users aremodulated, they must be combined and sent to the transmitter via thecombiner 420 for channelization and upconversion to MMDS frequencies. Atthe customer site 306, the signal after downconversion and filteringpasses through a sequence of operations that are essentially the reverseof those described above.

In order to take advantage of the current trend in chip designs for bothcable modems and for digital video transport over coaxial cable, the DVB(Digital Video Broadcast) compliant N-QAM chip sets can be selected forboth the digital broadcast video network as well as the two-way digitalnetwork.

Based on most areas in the United States, and because allowable averagetransmit digital power could be as high as 50 Watts per channel withcurrent equipment, 64 QAM is the preferred digital video modulation tocover the typical 35 mile protected service area. This is also thecurrent modulation level for most cable modems and coaxial cable videotransport. The corresponding capacity for the DVB 64 QAM isapproximately 27 Mb/s of information payload in a 6 MHz channel. Thiscorresponds to the equivalent of 890 Mb/s for the system bitratecapacity or over 295 three Mb/s digital video channels.

DVB 64 QAM can also be a potential selection for the smaller two-waycells 202 of FIGS. 2 and 3, depending on desired cell 202 size,robustness, and capacity tradeoffs. Because of the cross polarizationdesign and the smaller cell 202 array approach for two-way, even withmuch lower power transmitters, the margins could be made comparable tothe broadcast video service.

Functional block diagrams of the customer site 306 for both the digitalvideo and two-way services is shown in FIGS. 7A, 7B, and 7C.

FIG. 7A shows a system and method of reception of digital video at thecustomer site 306. The video signal from the horizontally polarizedreceive video antenna 308 of FIG. 5 is downconverted to the properfrequency range via the downconverter 500. Then it is filtered for theappropriate channel through the bandpass filter 502, and demodulated anddecoded through decoder 504. Since current television sets do notsupport digitally-compatible pictures, a settop box converts the signalvia conversion 506 into NTSC analog format such that the signal may beviewed on the television set 508.

FIG. 7B shows a system and method of reception at the customer siteafter data is received on the vertically polarized two-way antenna 310of FIG. 5. The data signal is downconverted in the downconverter 520,filtered through the appropriate bandpass filter 522, demodulated, anddecoded in the decoder 524. At that point, the bit stream can be passedto a customer device such as a computer or a telephone.

FIG. 7C shows a system and method of the uplink path from the customerdata device (e.g., computer) to the vertically polarized two-way antenna310. The data is encoded and modulated in the encoding and modulationdevice 552. It is then upconverted through the upconverter 550 to anappropriate frequency at the appropriate range (see FIG. 3), based onits location.

A summary example link budgets for both the digital video service andthe two-way data/telephony are shown in FIG. 8. Because the broadcastvideo source is the primary source of revenue for MMDS operators, it isassumed in this example that the data network will be designed with muchless powerful transmitters in order to minimize interference with thevideo signals. Therefore, for the purposes of the example link budget,0.5 W (equals 27 dBm) per 6 MHz channel for the data service is assumed.Of course, another option open to the operator is to transmit both thevideo and data signals from the transmit location on their respectivetransmitters.

The free-space loss (in dB) of the signal is given by 35.86+20 log(f(GHz)*1000)+20 log (D(miles)). The additional losses due to otherradio-frequency interference, rain and aiming mismatch, are assumed tobe small for the data network design. The noise power (in dBm) at thereceiver is given by -114+10 log B, where B is the radio-frequencybandwidth of a specific channel (in MHz). Note that in both cases, thesignal-to-noise ratio is preferably sufficient to maintain high qualityvideo and data communications for modulation schemes using 64-QAM orlower in order. As an example, DVB 64-QAM modulation, with (204, 188,T=8) Reed-Solomon error-control coding, requires 24.5 dB to achieve a1×10⁻⁹ corrected bit error rate (BER).

The two-way system design could carry any type of digital service:telephony, videoconferencing, internet traffic, high speed images, etc.The multiple access method could also be any number of choices such ascode division multiple access (CDMA), time division multiple access(TDMA), or frequency division multiple access (FDMA).

Although the present invention has been described in accordance with theembodiments shown, one of ordinary skill in the art will readilyrecognize that there could be variations to the embodiments and thosevariations would be within the spirit and scope of the presentinvention. Accordingly, many modifications may be made by one ofordinary skill in the art without departing from the spirit and scope ofthe appended claims.

We claim:
 1. A method for distributing information in a MMDS networkcomprising:a) providing a video signal in a first polarization to afirst area, the video signal having a frequency within a predeterminedspectrum of frequencies; and b) providing a two-way digital signal in asecond polarization to the first area, the two-way digital signal havinga frequency within the predetermined spectrum of frequencies, and thetwo-way digital signal being modulated by a high order modulation whichincludes one of a quadrature amplitude modulation (N-QAM) and avestigial side band (N-VSB), wherein the second polarization isorthogonal to the first polarization to minimize interference betweenthe two-way digital signal and the video signal.
 2. The method of claim1, wherein the spectrum of frequencies is a set of MultichannelMultipoint Distribution System frequencies.
 3. A method for distributinginformation in a MMDS network comprising:a) providing a video signal ina first polarization to a first area, the video signal having afrequency within a predetermined spectrum of frequencies; and b)enabling cellular digital data communication between the first area anda second area using a two-way digital signal in a second polarizationhaving a frequency within the predetermined spectrum of frequencies, thetwo-way digital signal being modulated by a high order modulation whichincludes one of a quadrature amplitude modulation (N-QAM) and avestigial side band (N-VSB).
 4. The method of claim 3, wherein thepredetermined spectrum of frequencies is a set of MultichannelMultipoint Distribution System frequencies.
 5. The method of claim 3,wherein the first polarization is orthogonal to the second polarizationto minimize interference between the two-way digital signal and thevideo signal, and wherein the two-way digital signal is substantiallyautonomous from the video signal for allowing both, the two-way digitalsignal and the video signal, to use the entire spectrum of frequenciessubstantially simultaneously.
 6. The method of claim 3, wherein thefirst area includes a plurality of sub-areas.
 7. The method of claim 6,wherein the plurality of sub-areas use varying frequency bands withinthe predetermined spectrum of frequencies.
 8. The method of claim 6,wherein the plurality of sub-areas areas divided into groups such thateach sub-area in a group uses a frequency band different from all otherfrequency bands used by the other sub-areas in that group.
 9. The methodof claim 6, wherein each sub-area is divided into a plurality of sectorssuch that each sector has its own frequency band.
 10. A system fordistributing information in a MMDS network comprising:means fortransmitting digital video signals having a first polarization and afirst frequency within a predetermined spectrum of frequencies; meansfor receiving the digital video signals; means for transmitting two-waydigital signals having a second polarization, the two-way digital signalbeing modulated by a high order modulation which includes one of aquadrature amplitude modulation (N-QAM) and a vestigial side band(N-VSB), the two-way digital signals having a second frequency withinthe predetermined spectrum of frequencies; and means for receiving thetwo-way digital signals.
 11. The system of claim 10, wherein the meansfor receiving the two-way digital signals is located within a predefinedarea in which the means for receiving the video signals is located. 12.The system of claim 10, wherein the spectrum of frequencies is a set ofMultichannel Multipoint Distribution System frequencies.
 13. The systemof claim 10, wherein the first and second polarizations are orthogonalto each other to minimize interference between the two-way digitalsignal and the video signal, and wherein the two-way digital signal issubstantially autonomous from the video signal for allowing both, thetwo-way digital signal and the video signal, to use the entire spectrumof frequencies substantially simultaneously.
 14. A system fordistributing information in a MMDS network comprising:a digital videosignal transmitter, wherein the video signal has a first polarizationand a first frequency within a predetermined spectrum of frequencies; adigital video signal receiver at a receiver site; a two-way digitalsignal transmitter, wherein the two-way signal has a second polarizationand a second frequency within the predetermined spectrum of frequencies,the two-way digital signal being modulated by a high order modulationwhich includes one of a quadrature amplitude modulation (N-QAM) and avestigial side band (N-VSB); and a two-way digital signal receiver atthe receiver site.
 15. The system of claim 14, wherein the first andsecond polarizations are orthogonal to each other to minimizeinterference between the two-way digital signal and the video signal,and wherein the two-way digital signal is substantially autonomous fromthe video signal for allowing both, the two-way digital signal and thevideo signal, to use the entire spectrum of frequencies substantiallysimultaneously.